For some time now the sophistication of computer graphics together with high-resolution monitors or visual display units (VDUs) has permitted engineers and designers to create and manipulate computer-generated virtual models instead of using conventional drawing board techniques. By a "virtual model" is meant data which results in an image corresponding to an object having apparent spatial coordinates relative to the viewer. This image is referred to as a "virtual image".
Since the early 1970's, with the evolution of computer-aided design (CAD) the promise of true three-dimensional (3-D) computer model representation has then the key to advanced manufacturing technology. The enhanced "realism" of virtual image also has considerable application in the entertainment industry. Computer games and arcade machines have greater customer appeal with improved graphic displays, and there is considerable competition in this field to bring in new "generations" of such machines.
The principal limitation of all conventional computer graphic displays is that virtual models are shown as flat images on a visual display unit (VDU) or television screen. "Visual depth cues" in the flat image may aid in perceiving it as three-dimensional. In computer graphics a variety of cues such as kinetic and static interposition, perspective projection and hidden line removal are commonly used, but the 3-D image is always perceived as a flat view (e.g. as in photograph) having no spatial realism. Consequently users of CAD equipment such as engineering designers, still restort to traditional techniques based on the drawing board, such as plan views and side elevations, as an aid to alignment of their 3-D descriptions.
As an improvement upon such displays it has been proposed to move a visual diaplay unit (VDU) within the area in which a computer-generated, virtual model has a mapped coordinate position. The computer is programmed to transmit to the movable VDU an image of the model as seen from the current position of the VDU. To achieve this the current position of the VDU was detected by the triangulation of sonar pulses. Taking a fixed point 40 cm in front of the VDC screen as the position of the viewer's focus, his current line of sight was transmitted to the computer according to the user's spatial position and the orientation of the VDU. In this way the user could move around the location in space given to a computer-generated virtual model and "see" it from all angles on the VDU that he steers in front of him.
Furthermore the image perceived was stereoscopic. The user wore a helmet with a rotating shutter stereo decoding device. Two images were calculated from positions corresponding to the separation of the user's eyes and transmitted to the VDU by the computer.
One drawback of this system is the need for the user to move around with him, e.g. on a trolley, the VDU he is looking at. Another is that the screen image does not wholly fill the user's field of view that he can be distracted by real surroundings. More importantly, however, a stereoscopic image on a flat screen seen through a decoder does not achieve as realistic a three-dimensional effect as when a different image is received by each eye (as in real life).